TRENTON, N.J. — Among the casualties of the Iraq war is a little-known religious faith called Mandaeanism that has survived roughly two millennia and whose adherents believe that John the Baptist was their great teacher.

While there were more than 60,000 Mandaeans in Iraq in the early 1990s, only about 5,000 to 7,000 remain. Many have fled amid targeted killings, rapes, forced conversions, and property confiscation by Islamist extremists, according to a report released last week by the New Jersey-based Mandaean Society of America.

Among the roughly 1,500 U.S. Mandaeans, there have been continual phone calls with endangered friends and relatives, collections of money, and unsuccessful lobbying efforts in Washington to get Mandaeans out of Iraq, as well as neighboring Jordan and Syria.

“Unfortunately, we’re not big in numbers, and numbers talk,” said Dr. Suhaib Nashi, a 53-year-old pediatrician who helps run the Mandaean Society of America out of his Morristown home.

Mandaean leaders say tens of thousands of their brethren are now scattered around the world, including a U.S. community located in New York and Detroit.

With the dispersion comes concern that the faith is withering, especially as more Mandaeans marry non-Mandaeans, with no mechanism to bring their children into the fold.

“There’s not much hope for us to survive to two or three generations,” Dr. Nashi said.

Scholars who study the Mandaean religion and culture say its extinction would be a great loss, the end of an ancient religious movement. Dating to the time of the Roman Empire, it survived primarily in what is today Iraq and Iran, a branch of the Gnostic movement that borrowed elements of Christianity.

Mandaeans view John the Baptist as a great teacher, and engage in baptisms to come in closer contact with a “world of light” that is better than the material world on Earth.

“It represents a slice of the culture of the Middle East before the rise of Islam. It’s a view to a former world. And frankly, we don’t know very much about it,” said Charles G. Haberl, an instructor in Middle Eastern studies at Rutgers University.

Mr. Haberl, who says he is trying to arrange a reprint of one of the Mandaeans’ main holy books for the first time in about 150 years, laments that an “enormous literary tradition” may soon disappear.

“It would be as if a museum or library were put to the torch,” Mr. Haberl said.

Driven from both Iraq and Iran, many Mandaeans have adapted to their new homes, having financial success as medical doctors, civil engineers and jewelers, Dr. Nashi said.

But being scattered means that many in the younger generation have found spouses outside the community. And because a Mandaean has to be born a Mandaean, the children of such marriages have a questionable status in the religion.

Mamoon Aldulaimi, 60, of Lake Grove, N.Y., is a civil engineer who’s a leader in the Mandaean community. Mr. Aldulaimi’s son, 20-year-old Hani Aldulaimi, married an American raised as a Baptist.

At the wedding last May in the Phoenix area, where the newlyweds live, Mamoon Aldulaimi’s daughter-in-law prominently displayed a darfash, a cross with cloth hanging off of it that’s a symbol of Mandaeanism.

“She took that initiative as a matter of respect for us,” Mr. Aldulaimi said.

But with the religion’s few dozen priests reluctant to agree on a mechanism to bring in the children of mixed marriages, Mr. Aldulaimi and others wonder how long Mandaeanism will survive.

Meanwhile, the few thousand Mandaeans still living in Iraq are finding their lives increasingly in danger, targeted by extremists of every political stripe and religious faith.

Dr. Nashi said a cousin on his father’s side, Suhail Jani Sahar, was killed by Shi’ite fighters in November. A more distant cousin on his mother’s side, Yahya Al-Chuhaily, was killed by Sunnis in June.

“Where there are areas where the Shia are the majority, they’ll kill the Mandaeans and the Christians along with the Sunnis. Where there are areas where the Sunni are the majority, they’ll kill the Mandaeans and the Christians along with the Shia,” Dr. Nashi said.

Both Dr. Nashi and Mr. Aldulaimi are convinced that there will soon be no Mandaeans left in Iraq.

Thousands of Mandaeans, they said, have taken refuge in Jordan and Syria but are still suffering abuses, with no easy way to escape to countries such as the United States, where they would be safe.